A former custodial worker at an elementary school in Brooklyn was arrested on charges of sexual abuse yesterday, officials from the Special Commissioner of Investigation for the New York City School District said.

The man, identified as Francisco Diaz, 57, was charged with forcibly kissing his niece on the mouth about 10 times, including incidents inside the school building of P.S. 219 on Clarkson Avenue in East Flatbush, where he worked tending to the boiler and the ventilation, and in the bedroom of his apartment. A report by the special commissioner, Richard Condon, alleged that Mr. Diaz also sexually abused two other nieces.

“This is completely reprehensible conduct, and Francisco Diaz should be prosecuted to the full extent of the law,” the schools chancellor’s counsel, Michael Best, said in a statement. “We will never allow him to work in our schools or be near our children again.”

The special commissioner’s office first learned of the alleged abuse after the father of the girl who said she had been forcibly kissed made a report. The father and his brother interrogated Mr. Diaz on their own after the girl told her mother what had happened, the report says. After he was confronted, Mr. Diaz allegedly confessed on tape that he had kissed the girl, the report says.

When officials from the special commissioner’s office interviewed Mr. Diaz, he confessed to having had extensive sexual contact with one of his other nieces as well some contact with a third niece, the report says. The second cousin alleged she was sexually abused about 30 times over a period of six years, the report says. The alleged conduct went far beyond kissing, and Mr. Diaz would often tell her to “be quiet” and say what was happening was her fault, the report says.

In the interview with the special commissioner’s investigative team, Mr. Diaz allegedly said that while he found sexual contact with his nieces sexually gratifying, he felt guilty about it, the report says.

The incidents involving the two other nieces are not being tried because they occurred too long ago, Mr. Condon said. Before 1996, under the statute of limitations in New York State, the five-year period in which sexual-abuse charges must be brought would begin at the time of the incident, according to the executive director of the New York State Coalition Against Sexual Assault, Anne Liske. Under legislation enacted in 1996, the five-year period begins when the child first reports the incident or turns 18, whichever occurs first, she said.

According to the Brooklyn district attorney’s office, Mr. Diaz is being charged with 18 counts of sexual abuse and with endangering the welfare of a child, all misdemeanors. If convicted he stands to face a maximum of one year on each count of sexual abuse.